How Tab Tender calculates a fair split

The method behind every tab — no black box.

Short answer

Tab Tender adds up what each person ordered, then splits tax, tip, and service in proportion to each person's share of the subtotal. Everyone pays for their own items plus their fair slice of the extras — and every share always sums back to the real bill total.

Splitting a bill evenly is fast, but it overcharges whoever ordered least. Tab Tender is built around a fairer rule that's still effortless at the table. Here's the exact method — including the math — so you can trust the number on your screen.

The core rule

Itemise.Each line item is assigned to the person (or people) who had it, so we know everyone's personal subtotal.
Allocate the extras proportionally. Tax, tip, and any service charge are split by each person's share of the subtotal — not evenly. If your food was 30% of the subtotal, you pay 30% of the tax and tip.
Reconcile. The per-person totals are checked back against the real bill so they always add up to the exact total — never a cent more or less.

A worked example

Three friends share a $128.00 bill: a $100.00 subtotal, $8.00 tax (8%), and a $20.00 tip (20%). Here's how Tab Tender divides it.

Person	Their items	Subtotal	Share	+ Tax & tip	They owe
Alex	Steak $32, cocktail $14	$46.00	46%	$12.88	$58.88
Bea	Salad $16, wine $12	$28.00	28%	$7.84	$35.84
Cam	Pasta $22, soda $4	$26.00	26%	$7.28	$33.28
Total		$100.00	100%	$28.00	$128.00

Splitting the same $128.00 bill evenly would charge everyone $42.67. That quietly overcharges Bea and Cam — who ordered less — while undercharging Alex, who ordered most, by $16.21. Proportional splitting fixes that automatically, and the three shares still sum to exactly $128.00.

The formula

For each person, their share of every add-on is:

person's add-on share =
   (their item subtotal ÷ bill subtotal) × (tax + tip + service)

amount they owe =
   their item subtotal + their add-on share

Because every share uses the same ratio, the add-ons are distributed completely and the per-person totals always reconcile to the real bill.

How the tricky cases are handled

Real bills aren't always clean. Tab Tender keeps the same balance-to-the-total guarantee through the messy parts:

Shared and uneven items. A shared plate is divided between everyone who had it — equally, or by units (6 of 10 wings to one person) or a percentage (75/25). The split always totals the item's exact price.
Pre-payments. If someone paid part up front (a deposit, the Uber), it's subtracted from what they owe; any overpayment shows as a refund the group owes them, or can be spread to lower everyone else's share.
Discounts.A whole-bill discount (a coupon, happy hour) is spread proportionally, just like tax and tip. A per-person comp (the birthday entrée) is absorbed on that one line without throwing off anyone else's math.
Covering someone. Mark a guest of honour as covered and their whole share is lifted off them and redistributed across everyone else — they keep their items on the record but pay $0, and the bill still balances.
Rounding. Money is tracked to the cent and any sub-cent rounding remainder is reconciled so the sum of the shares equals the printed total exactly — no mystery penny.
Currency. Each tab carries its own currency, so a trip abroad formats and rounds correctly.

Let Tab Tender do the math

Snap the receipt, tap who had what, and share a clean per-person summary with pay links — the proportional math happens for you.

Start a tab Read the tax & tip guide